Such an apparatus is known from WO2009/123452 in the name of the applicants. This known apparatus is used for separation of particles of rather small dimensions. The separation of the particles by this known apparatus is achieved by accelerating the moist particles in the particle-stream by the plates of the rotor impinging on said particles during their falling to the rotating drum. This results in a breakup of the particles of the first fraction from the particles of the second fraction that—due to their being moist—initially stick to each other. After their breakup the particles of the first fraction and the particles of the second fraction can freely and individually follow their flight and be collected in different receiving areas. In practice however the separation will not be perfect and the receiving area for the particles of the second fraction will receive also some particles from the first fraction, and the receiving area for the particles of the first fraction will also receive some particles of the second fraction.
The instant invention has as an objective to improve the known separation-apparatus in its function to separate from the particle stream a first fraction and a second fraction, wherein the fractions differ from each other only modestly in terms of the parameters that characterize the particles of said fractions. Like is the case for the known apparatus, this can be explained with reference to bottom-ash of waste incineration plants, although the invention is not restricted thereto.
The November-December 2007 issue of Waste Management World, pages 46-49, elaborates on bottom ash from such waste incineration plants as being by far the largest residue fraction after the incineration process. Due to the conditions of incineration, various materials including metals are comprised in the bottom ash. However, temperatures during the waste incineration process are generally not as high that these materials result in aggregated particles of metals with slag. Instead some 80% of the metals in the ashes are free and suited for re-use. It is said that with a particular type incinerator approximately 50% of the course bottom ashes consist of particles being larger than 2 mm. Conversely, another 50% of the materials is smaller than 2 mm. Particularly, the separation of particles which can be classified as part of a first fraction having dimensions smaller than 2 mm from particles being classified in a fraction having dimensions larger than 2 mm is a good example of the problems that are encountered when their separation is envisaged in a separation apparatus according to the preamble. Since the problems and the objectives that are connected with the separation of said first and second fractions from a particle-stream originating from bottom ash are very illustrative for the invention, the following discussion primarily utilizes the example of processing of bottom ash. It is expressly noted however that the separation-apparatus is not exclusively useable for processing of bottom ash but can be applied to process any type of particles having small dimensions.
On average, in the composition of bottom-ash aggregates of stone, glass and ceramics account for approximately 80% percent of its content and 7 to 18 percent account for ferrous and non-ferrous metals, whereas the remainder generally consists of organic material.
The main non-ferrous metal is aluminium which is present through the entire particle size range of the ash. Other non-ferrous metals are copper, brass, zinc, lead, stainless steel and precious metals which account for large parts of the 1-6 mm fraction or higher up to 15 mm. Such metals that originate from electronic components are largely in the 0-2 mm fraction.
As already mentioned above it is an objective of the invention to provide a separation-apparatus which is particularly suitable for carrying out a separation-method on a particle stream having particles in the ranges just mentioned.
It is a further objective to provide such a separation apparatus and method of its operation, which is applicable to particles that are moist. When the separation-apparatus is to be applied with respect to bottom ash an additional problem is that such bottom ash is relatively wet; it may comprise 15-20 weight % water.
A further objective is to provide a separation-apparatus which renders it possible to regain ferrous and non-ferrous metals of a particle stream with particles having dimensions in the range 0-15 mm.
Still a further objective is to provide such a separation-apparatus in which a first fraction and a second fraction of particles can be separated from a particle stream, wherein the first fraction has particles with a size in the range 0-2 mm and the second fraction has particles with dimensions in the range 2-15 mm.
DE-A-24 36 864 discloses a method in which a ballistic separation is carried out in order to regain thermoplastic particles from domestic waste. DE-A-24 36 864 uses for this purpose an apparatus in accordance with the preamble of the main claim. This known apparatus has a rotor placed in a housing, which rotor has radially extending plates that hit freefalling particles in order to have them follow ballistic trajectories that depend on the particle's specific surface area.
WO2004/082839 discloses a method for the recovery of non-ferrous metal-comprising particles from a particle stream consisting preferably for >90% by weight and more preferably for >98% by weight of particles having a size of <8 mm, yielding a non-ferrous metal-enriched fraction and a non-ferrous metal-depleted fraction, which method comprises the steps of:                a) putting the particle stream onto a conveyor belt in the form of a monolayer such that with the aid of a liquid, at least the non-ferrous metal comprising particles will adhere to the conveyor belt;        b) subjecting the moist mono-layer on the conveyor belt to a magnetic field rotating in the same direction as the belt, for the separation of non-ferrous metal-comprising particles, yielding the non-ferrous-enriched fraction, and        c) removing the particles adhering to the conveyor belt, yielding the non-ferrous metal-depleted fraction.        
The liquid content of the particle stream on the conveyor belt is, for example, ≧5%, such as ≧10%, and advantageously ≧12%, in relation to the total weight of the particle stream on the conveyor belt. In an example pertaining to the separation of nonferrous metals from bottom ash, a sifting operation resulted into a 50μ-2 mm fraction and a 2-6 mm fraction, whereafter the 2-6 mm fraction was subjected to a treatment with a rotary drum eddy-current separator.
EP-A-1 676 645 discloses an apparatus and method to sort a stream of mingled paper and plastic items. The items are fed by a conveyor to a release area spaced above a hitting area to which the items are falling, and from where the items are hit by hitting blades that are moved through the hitting area in a direction that diverges from the falling direction of the items. The items are collected in several receiving windows remote from the hitting area, each window corresponding to one of several fractions of the original stream of paper and plastic items.
DE-A-43 32 743 discloses a separation apparatus that is placed in a housing.